Electronic circuit board

ABSTRACT

An electronic circuit board having an optical wiring layer sandwiched between two electrical wiring layers. The optical wiring layer is structured to be a two-dimensional optical waveguide. An E/O device and an O/E device are provided in the optical wiring layer or at an interface between the optical wiring layer and the electrical wiring layer. A via piercing the optical wiring layer connects the two electrical wiring layers. It is possible to efficiently input and output light to and from an optical wiring layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic circuit board capable ofhighly densely mounting LSI chips such as CPU, memory, and the like.More specifically, the present invention relates to an opto-electroniccircuit board (or an optical integrated circuit board) having anelectrical wiring layer and an optical wiring layer.

2. Related Background Art

A cellular phone and a portable digital assistant (PDA) need to providehigh-speed processing and compactness or light weight at the same time.However, it is pointed out that accelerating the processing speedincreases the influence of wiring delay in the electronic circuit board.To minimize this influence, the simplest method is to make the wiring ina chip and between chips as short as possible. Since it can alsominiaturize circuit boards, many inventions have been made for thispurpose.

As the processing speed increases, however, another problem appears,i.e., a noise due to electromagnetic interferences (EMI).

Since electronic parts are arranged very closely to each other, thewiring becomes shorter but the wiring density becomes higher. When ahigh-speed signal is applied to adjacent signal lines, electromagneticwaves interfere with each other due to the mutual electromagneticinduction, causing a noise. As a result, the signal cannot betransmitted correctly. Mobile terminals, in particular, are more andmore designed for low voltages, and are consequently driven with a largecurrent, increasing effects of EMI.

This phenomenon means that the mobile terminal is susceptive to theexternal radio environment, i.e. so-called immunity or electromagneticcompatibility (EMC). That is, the fact that the mobile terminal itselfeasily generates EMI means that it easily sense an externalelectromagnetic field. Accordingly, normal data processing isunavailable depending on the radio environment.

Usually, these problems are solved by multilayering a ceramic substrateand enhancing EMC (i.e. electromagnetic compatibility) for each layer.However, it raises problems about costs and yield ratios, while it isessentially impossible to provide an EMI-free environment.

On the other hand, there is proposed a method of using optical wiringthat essentially has an advantage of no electromagnetic induction.

According to Japanese Patent Application Laid-Open No. 9-96746 (“Activeoptical circuit sheet or active optical circuit board” by Yoshimura etal.), for example, an optical wiring section is separated from anelectrical wiring section. Based on a signal voltage from an electronicinstrument, an optical switch or an optical modulator converts anelectric signal into an optical signal for transmission. The opticalsignal is reconverted into an electric signal by a light receivingelement that is provided at a different position in the optical wiringsection. Thus, an electric connection is made with another or the sameinstrument.

This method excels in compensating the demerit of the electrical wiringfor the optical wiring. Since the optical wiring uses a one-dimensionaloptical waveguide (or fiber), however, it is necessary to predetermine aposition for optical wiring. Further, the size for the optical wiringbecomes much larger than that for the equivalent electrical wiring.

According to Japanese Patent Application Laid-Open No. 11-196069(“Optical signal transmission apparatus, optical signal transmissionmethod, and signal processing apparatus” by Sakai et al.), the signallight input/output section is arranged at each of both opposite ends ofthe two-dimensionally extending optical sheet bus. An optical signal istwo-dimensionally transmitted in the optical sheet bus from one end. Thelight receiving element at the other end converts the optical signalinto an electric signal. This method solves conventionally inevitabledelays and transmission speed limitations in the electrical wiring andprovides easy mounting. There are arranged a transmission device (e.g.,one-dimensional semiconductor laser array) and a reception device (e.g.,one-dimensional photodiode array) at both ends of a two-dimensionaloptical waveguide called an optical sheet (having a waveguide structureonly in the thickness direction).

The signal operation is summarized as follows. A logic signal from theelectric circuit directly drives the semiconductor laser to convert theelectric signal into the optical signal. The generated light propagatesinside the optical sheet. At this time, the light is guided in thethickness direction and freely propagates in the plane directionperpendicular thereto. As a result, through the necessary optical powerbecomes larger than the conventional one, to increase the load to theelectrical circuit, tolerances for mounting the optical sheet andoptical devices become much larger. This method also solvesconventionally inevitable delays and transmission speed limitations inthe electrical wiring.

SUMMARY OF THE INVENTION

However, the above-mentioned technology relates to inter-instrumentwiring (bus line). No suppressing effects on EMI generated from acircuit board that mounts various electronic devices is expected. Thetechnology concerns the wiring (bus line) between instruments and givesno consideration to connection of an electronic device at a givenposition to any other electronic devices in the same instruments.

It is premised that light enters the end of the optical sheet. Noconsideration has been given to supplying light perpendicularly to theoptical sheet. As the inventors examined the entry of light into anoptical sheet, it was found that efficiently supplying light isdifficult just by providing a light emitting section on the opticalsheet.

It is therefore an object of the present invention to provide anelectronic circuit board capable of efficiently supplying lightperpendicularly to the optical sheet, not from its end. It is anotherobject of the present invention to provide an electronic circuit boardcapable of efficiently receiving the signal light propagated in theoptical sheet

An electronic circuit board according to the present invention has anoptical wiring layer sandwiched between two electrical wiring layers,wherein the optical wiring layer is structured to be a two-dimensionaloptical waveguide; an E/O (electrical-to-optical signal conversation)device and an O/E (optical-to-electrical signal conversation) device areprovided in the optical wiring layer or at an interface between theoptical wiring layer and the electrical wiring layer; and a via piercingthe optical wiring layer connects the two electrical wiring layers.

It is preferable that at least one of the E/O device and the O/E deviceis spherical, circular, or columnar.

Further, it may be preferable that the electrical wiring layer includesa parallel signal line with an output terminal connected to the E/Odevice; and a parallel electrical signal transmitted in the parallelsignal line is parallel-serial converted in an electronic circuitprovided in the E/O device and is then is then transmitted as a serialoptical signal to the optical wiring layer.

Moreover, it may be preferable that the serial optical signal isreceived by the O/E device, then is converted into an electrical signal,then is serial-parallel converted by an electronic circuit provided inthe O/E device, and is then transmitted to a parallel signal line.

The present invention makes it possible to efficiently input or outputoptical signals by providing the E/O device and the O/E device insidethe optical wiring layer or at an interface between the optical wiringlayer and the electrical wiring layer. The E/O device and the O/E deviceare so-called opto-electric conversion devices. The followingdescription primarily refers to the use of a spherical opto-electricconversion device but is not limited thereto only if it is possible toinput or output light to the optical wiring layer.

The electronic circuit board according to the present invention has alayered structure unit comprising two layers: an electrical wiring layerand an optical wiring layer. A plurality of electronic devices arearranged on the surface or inside of the circuit board. The electricalwiring layer includes electrical wiring that electrically connects theelectronic devices with each other. The optical wiring layer isstructured to be a film-shaped two-dimensional optical waveguide. TheE/O device and the O/E device are provided in the electrical wiringlayer, the optical wiring layer, or an interface between them. The E/Odevice converts an electrical signal from the electronic devices into anoptical signal and transmits the optical signal into the optical wiringlayer. The O/E device receives the optical signal and converts it intoan electrical signal. In addition, the electrical connection to the E/Oand O/E devices is made from the electrical wiring layer side.

In the electronic circuit board, there may be formed a plurality of viasthat pierce the optical wiring layer and electrically connect theelectrical wiring layers sandwiching the optical wiring layer. On aspherical semiconductor substrate, together with other electronicdevices, there may be formed the E/O device that converts an electricalsignal from an electronic device into an optical signal and transmitsthe optical signal into the optical wiring layer. On a sphericalsemiconductor substrate, together with other electronic devices, theremay be integrated and formed the O/E device that converts an opticalsignal transmitted in the optical wiring layer into an electricalsignal.

The electronic circuit board may have a parallel signal line whoseoutput terminal is connected to the E/O device. The electronic circuitof the spherical device may perform a parallel-serial conversion totransmit a serial optical signal to the optical sheet. It is alsopossible to receive the serial optical signal at the O/E device embeddedin the optical sheet. After the optical signal is converted into anelectrical signal, the signal may be serial-parallel converted in theelectronic circuit formed together on the spherical semiconductorsubstrate. The converted signal can be transmitted to a parallel signalline. The electronic circuit board can be configured with a flexiblematerial.

Further, the electronic circuit board according to the present inventionhas a multi-layered structure comprising a plurality of layers. A unitconstituting the multi-layered structure comprises two layers: anelectrical wiring layer and an optical wiring layer. A plurality ofelectronic devices are arranged on the surface or inside of the circuitboard. The electrical wiring layer includes electrical wiring thatelectrically connects the electronic devices with each other. Theoptical wiring layer is structured to be a film-shaped two-dimensionaloptical waveguide. The E/O device and the O/E device are provided in theoptical wiring layer. The E/O device converts an electrical signal fromthe electronic devices into an optical signal and transmits the opticalsignal in all directions of the optical wiring layer. The O/E devicereceives the optical signal from all directions in the optical wiringlayer and converts it into an electrical signal. In addition, theelectrical connection to the E/O and O/E devices is made from theelectrical wiring layer side.

In the electronic circuit board, there may be formed a plurality of viasthat pierce the optical wiring layer and electrically connect theelectrical wiring layers sandwiching the optical wiring layer. The E/Odevice to convert an electrical signal from the electronic device intoan optical signal and to transmit the optical signal into the opticalwiring layer may be shaped like a disk or a column. The O/E device toconvert an optical signal transmitted in the optical wiring layer intoan electrical signal may be shaped like a disk or a column.

The electronic circuit board may have a parallel signal line whoseoutput terminal is connected to the E/O device. The electronic circuitof the spherical device may perform a parallel-serial conversion totransmit a serial optical signal to the optical wiring layer. It is alsopossible to receive the serial optical signal at the O/E device embeddedin the optical wiring layer. After the optical signal is converted intoan electrical signal, the signal may be serial-parallel converted in theelectronic circuit formed together with the device. The converted signalcan be transmitted to a parallel signal line.

(Operation)

When adjacent metal wirings provide high-speed data (e.g., 1 Gbps), theintensity of electromagnetic radiation noise nearby is expressed as:“generating source intensities (frequency, waveform, and drivecurrent)”×“transfer constants (resonance with the power supply line andconnection with an adjacent line)”×“antenna factors (connectors andelectrodes)”. That is to say, the noise level increases in proportionthat the wiring length becomes longer, the electrical current amountincreases, the signal speed increases, and the signal pulse approximatesto a rectangular wave. Therefore, it is basically impossible toeliminate EMI as long as the metal wiring is used near the CPU.

The use of optical wiring substantially solves these problems. That isto say, the optical wiring makes the transfer constant to be zerobecause no electromagnetic induction occurs.

On the other hand, however, the physical size per optical wiring is overten times larger than the electrical wiring as long as an opticalwaveguide is used. Replacing the entire electrical wiring with opticalwiring rather emphasizes demerits such as a significantly increasedsize, an increased loss due to bending, and the like. Further, the useof such optical wiring necessitates a change in the conventionalelectrical wiring pattern. As a solution to relieve these problems, itis proposed that the conventional pattern is used for electrical wiringand the optical wiring uses an optical film for transmission in thetwo-dimensional space. However, there is not yet presented an effectivesolution for a method of mounting an E/O device to convert an electricalsignal into an optical signal and an O/E device to convert an opticalsignal into an electrical signal. The present invention provides atechnology of mounting O/E and E/O devices on the opto-electroniccircuit board as an essential technology for embodying the solution.

The principal objective of the present invention is summarized asfollows.

(1) A two-dimensional optical waveguide (optical film) is used for anoptical waveguide as optical wiring to provide a multilayeredopto-electronic circuit board structure comprising a pair of electricalwiring layers and an optical wiring layer.

(For the opto-electronic circuit board, refer to File No. 202349, nowU.S. Pat. No. 6,897,430, “Opto-electronic wiring board, opto-electronicintegrated circuit, and method of manufacturing the same”.)

(2) A via is used for connection between a plurality of electricalwiring layers.

(3) The opto-electric conversion device to be used is a sphericalphotonic ball IC that comprises concurrent integration of an opticaldevice and its drive IC or an amplifier.

The opto-electronic circuit board comprises an ordinary electroniccircuit board or a printed circuit board (PCB) coupled with atwo-dimensional optical waveguide. The electrical wiring part complieswith the conventional technique. The optical wiring part uses thetwo-dimensional optical waveguide (optical film). This scheme solves theconventional problems that the optical wiring increases a wiring size,that the use of optical wiring has an effect on the electronic devicearrangement, and the like. Further, it permits free selection betweenthe electrical wiring and the optical wiring.

A via is a requisite means for the three-dimensional wiring. When theoptical wiring layer is used, a large demerit will result if the viacannot be formed at a desired position. Since the present invention usesa film-shaped optical waveguide, an optical signal diffusestwo-dimensionally to propagate even if the via is hence formed at anyposition. An effect of the via is hence negligible. Accordingly, it ispossible to introduce EMI-free optical wiring with no influence on theconventional design principle.

The flip-chip mounting or the BGA (Ball Grid Array) method is used as amounting method to facilitate the easy mounting without applying a newmounting method for optical wiring. The BGA method uses solder called abump to connect an electrode pad on the IC to an electrode pad on thecircuit board in an array. Compared to the conventional wire bonding,the BGA method excels in such characteristics as an increased speed, asmall area required, and a low resistance.

Typically, the BGA pitch and the solder ball diameter are sized to beapproximately 1 mm and 0.50 mm, respectively. When the photonic ball ICis 1 mm diameter or less, a BGA process can be used to easily satisfythe above-mentioned requirements.

The photonic ball IC is an integration of electronic devices and opticaldevices on a spherical semiconductor substrate (usually, a spherical Sisubstrate). A single photonic ball IC is capable of O/E or E/Oconversion. No additional circuit is needed when the photonic ball IC tobe used can be directly driven by a voltage of a logic signal from theLSI circuit formed in the opto-electronic circuit board. Since thephotonic ball IC is spherical, it can be optically coupled to an opticalfilm section of the opto-electronic circuit board without needing for aspecial optical system.

The following provides an overview of the photonic disk IC. (For detailson the manufacturing method and the like, refer to Japanese PatentApplication Laid-Open No. 10-262837, “Semiconductor laser capable ofpolarized wave modulation having ring resonator” or Japanese PatentApplication Laid-Open No. 2000-022285, “Opto-electronic device”.)

FIGS. 10A and 10B are schematic diagrams showing a ring resonator typesemiconductor laser, hereafter referred to as a ring LD (laser diode),as a simplest example of the photonic disk IC. The ring LD devicecontains a ring resonator. When light orbits in the ring resonator, thering LD obtains a gain to oscillate. In principle, light is confined inthe resonator, but is partially extracted to the outside. A circularresonator can irradiate light in 360 degree directions inside theresonator plane. When this ring laser is provided in the optical wiringlayer, the light can propagate inside the entire optical wiring layer.

The following explains the ring laser with reference to the accompanyingdrawings. FIGS. 10A and 10B are schematic diagrams of the ring laser.

FIG. 10A is a plan view. FIG. 10B is an elevational view with afragmentary cross sectional view taken along lines 10B—10B for the lefthalf. For example, the reference numeral 1301 represents an n-typesemiconductor substrate, 1302 an n-type AlGaAs clad layer, 1303 an MQWactive layer, and 1304 a p-type clad layer. There is formed aring-shaped resonator 1307 (e.g., 200 μm long) having a vertical, smoothside surface. A cathode 1305 and an anode 1306 are formed for carrierinjection. This laser is characterized as follows. When the carrierinjection reaches a given level, the gain exceeds a resonator loss ofthe ring laser, activating two orbit oscillation modes clockwise andcounterclockwise. Part of the laser beam (resonant beam 1308) can beextracted from the ring resonator side to the outside. A completelycircular ring laser can transmit a laser beam (output beam 1309) toalmost all the area at 360 degrees in the active layer plane of the ringlaser. Let us consider that the ring laser is enclosed in atwo-dimensional slab waveguide. In this case, when the anode and thecathode are superposed with an electrical signal at a level appropriateto the oscillation threshold value for the ring laser, the beam can bepropagated throughout the entire two-dimensional slab waveguide as anoptical signal.

On the other hand, the ring laser or a similar semiconductor device canoperate as a light receiver. The ring resonator side can be used as alight receiving surface that receives light beams propagating from alldirections in the plane where the ring resonator is placed. Applying anappropriate bias widens a depletion layer. This can improve the lightreceiving efficiency. The light receiver is hereafter referred to as aring PD (photodiode).

When arranged in the optical wiring layer, the ring PD can receive abeam propagating from all directions in the optical wiring layer and canconvert the beam into an electrical signal.

As described above, the light emitting and receiving functions can beprovided to a photonic device having almost the same structure.

Further, it is possible to directly convert a logic signal from otherLSI circuits into an optical signal or to directly convert an opticalsignal into an electrical signal by integrating electronic circuits suchas a drive circuit for the ring LD, a bias circuit for the ring PD, andan amplifier into that device. FIGS. 11A and 11B are schematic diagramsof the photonic disk device. FIG. 11A is a plan view with a fragmentarycross sectional view of the ring LD section for the left half. FIG. 11Bis an elevational view with a fragmentary cross sectional view takenalong lines 11B—11B for the left half. The ring LD section has almostthe same structure as shown in FIGS. 10A and 10B. It comprises an n-typeclad layer 1302, an active layer 1303, and a p-type clad layer 1304 toconstitute an optical device area 1402. The substrate is removed toprovide a thin film. The optical device area 1402 is sandwiched betweenSi device areas 1401 a and 1401 b having electronic circuits 1403thereon. Electrode pads 1105 are formed on the surface for input/outputoperations of a logic signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram for explaining an electronic circuit boardaccording to the present invention;

FIG. 2 is a schematic diagram for explaining signal transmission on theelectronic circuit board according to the present invention;

FIG. 3 shows a configuration example of a photonic ball IC used in thepresent invention;

FIG. 4 shows another configuration example of the photonic ball IC usedin the present invention;

FIG. 5 is an explanatory diagram for a method of mounting the photonicball IC used in the present invention;

FIG. 6 is a schematic diagram for explaining the electronic circuitboard according to the present invention;

FIG. 7 is a schematic diagram for explaining the electronic circuitboard according to the present invention;

FIG. 8 is a schematic diagram for explaining the electronic circuitboard according to the present invention;

FIGS. 9A, 9B, 9C, and 9D are schematic diagrams showing a manufacturingprocess of the electronic circuit board in FIG. 8;

FIGS. 10A and 10B show a configuration example of the photonic disk ICused in the present invention;

FIGS. 11A and 11B show another configuration example of the photonicdisk IC used in the present invention; and

FIG. 12 is a schematic diagram for explaining the electronic circuitboard according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Embodiment 1)

FIG. 1 is a sectional view of the electronic circuit board according tothe present invention. Photonic ball ICs are provided at upper and lowerinterfaces of an optical wiring layer.

In FIG. 1, the reference numeral 101 represents a circuit board base,103 a and 103 b electrical wiring layers, and 104 a film-shaped opticalwiring layer sandwiched between the electrical wiring layers. Thereference numeral 102 denotes an IC chip mounted on the surface of theelectrical wiring layer 103 b by means of bumps (e.g., solder balls)107. The reference numerals 108 a through 108 c represent photonic ballICs that are mounted at interfaces between the electrical wiring layers103 a and 103 b and the optical wiring layer 104. The reference numeral106 represents micro-strip lines formed in the electrical wiring layersor on the surface thereof. The reference numeral 105 representselectrode pads electrically connected to them. The reference numeral 109represents vias that make electrical connection between the electricalwiring layers through the optical wiring layer.

(Photonic Ball IC)

One of the features of the present invention is to use the E/O or O/Edevice for connection between the electrical wiring layers 103 a and 103b and the optical wiring layer 104. The following provides a briefdescription on the photonic ball IC as an example of the E/O or O/Edevice. (For details on the manufacturing method and the like, refer toJapanese Patent Application No. 2000-090826 Opto-electronic devicehaving a three-dimensional configuration”.)

In FIG. 3, the reference numeral 301 represents an undoped spherical Sisubstrate (e.g., 1 mm diameter). The reference numeral 302 represents anIC formed on its hemisphere surface (northern hemisphere surface in thisexample). The reference numeral 303 represents an optical device such asa light emitting element, a light receiving element, or the like formedon the southern hemisphere surface. (The optical device here is assumedto be a GaInNAs/AlGaAs based surface emitting laser or surfacephotodiode formed on four (111) equivalent surfaces but is not limitedthereto.) Electrical wiring 304 connects the above-mentioned componentswith each other.

When integrated with the light emitting element 303, the IC 302 may be adrive IC or a parallel-serial conversion circuit. When integrated withthe light receiving element 303, the IC 302 may be a bias circuit, apreamplifier, a waveform adjustment circuit, or a serial-parallelconversion circuit. Of course, when supporting both the functions,corresponding electronic circuits need to be added. These circuits canbe fabricated through a normal CMOS process. Its logic voltage is 3.3 V.

FIG. 4 shows another configuration of the photonic ball IC. Similarly tothe above-mentioned configuration, the electronic circuit sectioncontains electronic circuits 401, electrical wiring 402, electrode pads403 for the electronic circuits, and the like. However, the opticaldevice section is largely different. The reference numeral 405 denotes ahemispherical active layer. For the light emitting device, the activelayer 405 causes light emission due to recombination of carriersinjected from the electrodes 407 a and 407 b for the optical device. Forthe light receiving device, a reverse bias is applied to the activelayer 405. The received beam forms a pair of electron and hole. Ineither case, the photonic ball IC, because of its spherical shape, canhighly efficiently perform the E/O or O/E conversion without needing aspecial optical system for light emission and absorption. Outside theactive layer 405, there are formed a clad layer 404 and a contact layer406 in this order.

The following describes the manufacturing method.

(Electrical Wiring Layer)

In FIG. 1, the electrical wiring layer 103 a is first formed on thecircuit board base 101.

In this example, a hot-melt resin material (e.g., polyimide 0.3 mmthick) containing the Cu micro-strip lines 106 constituted of aplurality of layers is formed on the glass epoxy resin circuit boardbase 101.

(Mounting the Photonic Ball IC on the Electrical Wiring Layer)

Then, the photonic ball ICs 108 a and 108 c are mounted. The followingdescribes the mounting method of the spherical optical device withreference to FIG. 5. First, in order to mount the photonic ball IC, ahemispherical hole is dug at a specified position on the surface of theelectrical wiring layer. Any method can be used to dig the hole.

The hole may be formed by using photo-lithography and etching.Alternatively, the hole may be formed independently at any position byusing a laser processing apparatus or the like.

Here, an excimer laser is used to successively form holes 501 with aspecified shape at specified positions. This method can use CAD data asis for manufacturing the circuit board, ensuring accuracy in thetwo-dimensional directions and improved controllability in the depthdirection.

The electrode pads 403 of the ball IC 206 and the electrical wiring 106of the electrical wiring layer 103 a are to each other. An anisotropicconductive resin or the like is used to make an electrical andmechanical contact.

After this step, electrical wiring may be further provided on thesurface if needed.

(Manufacturing the Optical Wiring Layer)

The optical wiring layer may have any configuration if the followingconditions are satisfied.

(1) There should be a two-dimensional slab optical waveguide for guidinga beam.

A minimal transmission loss is preferable, however, depending on atransmission distance. When the circuit board is several centimeterssquare, for example, a transmission loss should desirably be 0.1 dB/cmor less for the wavelength of a beam to be guided.

(2) The electrical wiring layer should be able to be manufactured on thesurface.

This aims at using a conventional electrical wiring pattern as is.

(3) The mounted photonic ball IC should be able to be embedded.

For the present embodiment that satisfies these three points, an organicresin such as polyimide is applied and flattened to manufacture anoptical wiring layer comprising a film-shaped optical waveguideapproximately 1 mm thick. The embodiment uses a film-shaped opticalwaveguide comprising a single layer but is not limited to thisstructure. It may be preferable to use a slab waveguide structure inwhich a core layer (0.1 mm thick, refractive index n1) is sandwichedbetween clad layers (0.3 mm thick, refractive index n2, where n1>n2). Itis effective to successively form the second electrical wiring layer 103b (with the photonic ball IC).

According to the above-mentioned process, the first electrical wiringlayer 103 a, the optical wiring layer 104, and the second electricalwiring layer 103 b are layered on the circuit board base 101 as shown inFIG. 1. Finally, the IC chip 102 is surface mounted on the secondelectrical wiring layer 103 b via the solder bumps 107 and the like tocomplete the embodiment according to the present invention.

(Principle of Operations)

The following describes the principle of operations.

(Transmission Function)

In FIG. 1, the electrode pads 105 of the LSI 102 are connected to theelectrical wiring layer via the bumps 107 to transmit or receive anelectrical signal from a nearby electronic device. A logic signal fromthe LSI (e.g., 3.3 V for CMOS) provides a sufficient voltage to directlydrive the above-mentioned spherical optical device. When the logicsignal is applied to a light emitting device (e.g., LED) on the photonicball IC 108 a directly mounted on the electrical wiring layer 103 a sothat a forward bias is generated, the electrical signal is convertedinto an optical signal. (When power is required or a specified biasvoltage needs to be applied, it just needs to fabricate a driver circuitor a bias on the photonic ball IC 108 a.) The E/O converted opticalsignal is emitted to the optical wiring layer 104 and diffuses andpropagates as an output beam 110 to the entire optical sheet withoutneed for a special optical system. When the circuit board size isapproximately 30 mm□ and the transmission loss is 0.1 dB/cm or less, anoptical output of approximately 1 mW can sufficiently obtain a receptioninput needed for the minimum receiving sensitivity.

(Reception Function)

By contrast, an input optical signal 110 propagates from any directionof the optical wiring layer 104. When the optical signal 110 reachessurfaces of the light receiving elements of the photonic ball ICs 108 band 108 c, the optical signal 110 is introduced into the inside. Theoptical signal 110 is thus absorbed near a reversely biased PN junctionand is converted into an electrical signal. The converted electricalsignal works as an input electrical signal, and is introduced into theLSI 102 to be processed there via the adjacent electrical wiring layer103 b.

(Electro-parallel and Opto-serial Transmission)

The following describes the electro-parallel and opto-serialtransmission, one of actual examples, with reference to FIG. 2. In FIG.2, the reference numeral 202 represents a CPU, 203 a and 203 b RAMs, 204other electronic devices, 207 parallel electrical wiring formed in theelectrical wiring layer, and 208 optical wiring (optical path) in theoptical wiring layer 104.

Normal electrical wiring requires a 64-bit data line comprising sixtransmission paths. Even if low-speed data processing causes no problem,high-speed transmission of a large amount of data (e.g., motionpictures) is susceptible to influences of operations of the otherdevices arranged on the same circuit board or easily causes influencesof EMI. It is very difficult for the conventional wiring to alwaysconstantly transmit data. The optical wiring is used for this purpose.

In FIG. 2, for example, six electrical wiring lines are needed for the64-bit data transmission from the CPU 202 to the RAMs 203 a and 203 b.If the CPU performs a parallel-serial conversion at its last processingstage and one optical I/O element is connected thereto, the parallelelectrical signal is transmitted as a serial optical signal over theoptical waveguide of the opto-electronic circuit board. The opticalsignal is received and O/E converted at the receiving optical I/Oelement and then is serial-parallel converted to generate a 64-bitparallel electrical signal. While the parallel-serial conversionincreases the clock, propagation to the optical waveguide causes noproblems of EMI.

While the embodiment selects the optical wiring from the beginning, itis not necessary to always use only the optical wiring. When there isavailable an option of selecting the electrical wiring, it is possibleto make connection by means of the electrical wiring or the opticalwiring depending on needs. This flexibility is one of the majoradvantages of the present invention.

The electrical wiring may need to be designed to detour other devices inorder to avoid EMI. As a result, the wiring becomes long, causing wiringdelay or waveform distortion. In such case, selecting the optical wiringcan provide an EMI-free connection by the shortest route, causing nowiring delay nor waveform distortion. According to the embodiment, thevia 109 is formed by piercing the optical waveguide layer 104. Since anoptical signal propagates by diffusion, however, its influence isnegligible unless the via density becomes excessively large.

A device that manages the bus ultimately determines which signal shoulduse the electrical wiring or the optical wiring. The signal convertedinto a light beam propagates by diffusing in the optical wiring layerand approaches the IC arranged at a different location. Near this IC,there is also arranged the photonic ball IC 108 for O/E conversion. Theembodiment arranges the same photonic ball IC. Since its surface isspherical, the light is directly received by the pn junction surfacewithout using a prism or a mirror, making it possible to very easilymount the photonic ball IC.

(Effects)

(1) The optical wiring is available without making a large change in theconventional electrical wiring pattern.

(2) A method compliant with the conventional electrical mounting methodcan be used to mount the E/O device or the O/E device.

(3) The use of the two-dimensional optical waveguide layer (opticalfilm) on the circuit board enables free optical wiring, high-speedtransmission, and EMI-free transmission.

(4) The same signal can be transmitted over the electrical wiring or theoptical wiring depending on uses.

The following methods have been proposed to connect two-dimensionaloptical waveguides onto the surface:

(1) Methods of arranging mirrors and prisms such as “Optical connectionapparatus and method of manufacturing the same” (Japanese PatentApplication Laid-Open No. 8-220357) and SPIE OptoelectronicInterconnects and Packaging, CR62 (1996), 329; and

(2) Methods of arranging gratings and holograms.

However, these methods are liable to such problems as: 1) the opticalaxis alignment is difficult; 2) the number of parts increases; 3) theoptical waveguide requires micro-processing; 4) it is difficult toarrange devices at any desired positions because the optical waveguideneeds to be micro-processed; and 5) it is difficult to transmit orreceive an optical signal in any desired direction.

According to the embodiment, for example, a light beam from the lightemitting section is directly applied to the inside of the optical wiringlayer or to an interface between the optical wiring layer and theelectrical wiring layer. It is therefore possible to eliminate theproblem of the optical axis alignment and efficiently input or outputlight beams.

(Embodiment 2)

FIG. 6 schematically shows a sectional view of a second embodiment ofthe present invention.

Differences from the first embodiment are: (1) optical wiring layers 104a and 104 b are multilayered; (2) no circuit board base is used; and (3)electronic devices 102 a and 102 b are mounted on both surfaces. Themutually corresponding members in FIGS. 6 and 1 are designated by thesame reference numerals.

(Common Points)

(1) Each of the optical wiring layers 104 a and 104 b transmits data bydiffusing an optical signal two-dimensionally.

(2) vias are to connect electrical wiring layers 103 a through 103 cwith each other.

The embodiment is briefly supplemented as follows.

-   -   According to embodiment 1, the photonic ball ICs 108 are mounted        at specified positions on the surface of the electrical wiring        layer 103 a (e.g., PMMA).    -   The optical wiring layer 104 a is formed on the surface thereof.    -   The photonic ball ICs 108 are mounted on the second electrical        wiring layer 103 b which is then bonded to the optical wiring        layer.    -   Vias are provided at specified positions and are plated or        processed otherwise to make an electrical contact.

By repeating these four steps, it is possible to manufacture amultilayer electronic circuit board comprising alternately layeredelectrical wiring layers and optical wiring layers.

According to the embodiment, all the optical wiring layers comprise asheet-shaped optical waveguide. However, applicable examples are notlimited thereto. For example, it may be preferable to form aone-dimensional optical waveguide that confines light completely.

(Embodiment 3)

The ball IC is also used as a scatterer.

FIG. 7 is a schematic diagram for explaining the third embodiment. Themutually corresponding members in FIGS. 7 and 1 are designated by thesame reference numerals.

Main differences from the first embodiment are as follows.

(1) Optical scatterers 111 a through 111 c are arranged near thephotonic ball ICs 108 a through 108 c.

(2) When light is emitted, each optical scatterer functions as ascatterer to diffuse the light throughout the optical wiring layer 104.

(3) When light is received, each optical scatterer functions as acondenser to efficiently condenses the light to the light receiver justabove.

The embodiment is briefly supplemented as follows.

-   -   According to embodiment 1, the photonic ball ICs 108 a and 108 c        and the optical scatterer or condenser 111 b are mounted at        specified positions on the surface of the electrical wiring        layer 103 a (e.g., PMMA).    -   The optical wiring layer 104 is formed on the surface thereof.    -   The photonic ball IC 108 b and the optical scatterers (or        condensers) 111 a and 111 c are mounted on the second electrical        wiring layer 103 b which is then bonded to the optical wiring        layer 104.    -   The vias 109 are provided at specified positions and are plated        or processed otherwise to make an electrical contact.

By repeating these four steps, it is possible to manufacture amultilayer electronic circuit board comprising alternately layeredelectrical wiring layers and optical wiring layers.

A function of the optical scatterer is to reflect the light from thephotonic ball IC to an optical diffusion layer as much as possible.

Another function of the optical condenser is to condense the lightpropagating in the optical wiring layer into the vicinity of thephotonic ball IC as much as possible and improve the light receivingefficiency.

Both are specifically structured to be:

(1) Conical shape (having a high-reflectance surface);

(2) An aggregate of fine particles as small as the wavelength; or

(3) A ring-shaped grating element.

These belong to a known structure.

The embodiment uses an Si ball IC coated with a high-reflectance film inconsideration of not only the condensing efficiency and the scatteringefficiecy, but also ease of mounting and costs. The photonic ball ICitself may be used as a scatterer or a condenser.

An effect specific to embodiment 3 is to be able to manufacture anelectronic circuit board having high scattering and condensingefficiency.

(Embodiment 4)

A photonic disk IC is placed in the optical wiring layer.

FIG. 8 is a sectional view of a fourth embodiment of the presentinvention. In FIG. 8, the reference numeral 101 represents the circuitboard base, 103 a and 103 b the electrical wiring layers, and 104 thefilm-shaped optical wiring layer sandwiched between the electricalwiring layers. The reference numeral 102 denotes the IC chip mounted onthe surface of the electrical wiring layer 103 b by means of the bumps(e.g., solder ball) 107. The reference numerals 108 a through 108 crepresent photonic disk ICs that are mounted in the optical wiring layer104. The reference numeral 106 represents the electrical wiring (e.g.,the micro-strip lines) formed in the electrical wiring layer or on thesurface thereof. The reference numeral 105 represents the electrode padselectrically connected to them.

The following describes the manufacturing method with reference to FIGS.9A, 9B, 9C and 9D.

(Electrical Wiring Layer)

The electrical wiring layer 103 is first formed on the circuit boardbase 101.

In this example, a hot-melt resin material 103 (0.3 mm thick) containingthe Cu micro-strip lines 106 constituted of a plurality of layers isformed on the glass epoxy resin circuit board base 101. On its surface,there are formed the electrode pads 105 that electrically connects withthe O/E or E/O device (FIG. 9A).

(Mounting the Photonic Disk IC on the Electrical Wiring Layer)

Then, the photonic disk ICs 108 are mounted. The electrode pads of thephotonic disk ICs are aligned with the electrode pads 105 of theelectrical wiring layer. An anisotropic conductive resin, a solder ball,or the like is used to make an electrical and mechanical contact (FIG.9B).

(Manufacturing the Optical Wiring Layer)

The optical wiring layer may have any configuration and material if thefollowing conditions are satisfied.

(1) There should be a two-dimensional slab optical waveguide for guidinga beam.

(2) A transmission loss should be small.

A minimal transmission loss is preferable, however, depending on atransmission distance. When the circuit board is several centimeterssquare, for example, the transmission loss should desirably be 0.1 dB/cmor less.

(3) The mounted photonic disk IC should be able to be embedded.

For the present embodiment that satisfies these three points, an organicresin such as polyimide is applied and flattened to manufacture anoptical wiring layer 104 comprising a film-shaped optical waveguideapproximately 0.3 mm thick (FIG. 9C).

The embodiment uses the film-shaped optical waveguide comprising asingle layer but is not limited to this structure. It may be preferableto use a slab waveguide structure in which a core layer (0.05 mm thick,refractive index n1) is sandwiched between clad layers (0.1 mm thick,refractive index n2, where n1>n2).

The second electrical wiring layer 103 (with the electrode pad) is thenformed (FIG. 9D).

According to the above-mentioned process, the first electrical wiringlayer 103 a, the optical wiring layer 104, and the second electricalwiring layer 103 b are layered on the circuit board base 101 as shown inFIG. 8. Finally, the IC chip 102 is surface mounted on the secondelectrical wiring layer via the solder bumps 107 and the like tocomplete the embodiment according to the present invention.

(Principle of Operations)

The following describes the principle of operations.

(Transmission Function)

In FIG. 8, the electrode pads 105 of the LSI 102 are connected to theelectrical wiring layer 103 b via the bumps 107 to transmit or receivean electrical signal from a nearby electronic device. A logic signalfrom the LSI (e.g., 3.3 V for CMOS) provides a sufficient voltage todirectly drive the above-mentioned spherical optical device. When thelogic signal is applied to a light emitting device (e.g., LED) on thephotonic disk IC 108 a directly mounted on the electrical wiring layerso that a forward bias is generated, the electrical signal is convertedinto an optical signal 110. (When power is required or a specified biasvoltage needs to be applied, it just needs to fabricate a driver circuitor a bias on the photonic disk IC 108 a.) The E/O converted opticalsignal is emitted to the optical wiring layer 104 and diffuses andpropagates as an output beam 110 to the entire optical sheet withoutneed for a special optical system. When the circuit board size isapproximately 30 mm□ and the transmission loss is 0.1 dB/cm or less, anoptical output of approximately 1 mW can sufficiently obtain a receptioninput needed for the minimum receiving sensitivity.

(Reception Function)

By contrast, an input optical signal 110 propagates from any directionof the optical wiring layer 104. When the optical signal 110 reaches thesurface of the light receiving element of the photonic disk IC, theoptical signal is introduced into the inside. The optical signal isabsorbed near a reversely biased PN junction and is converted into anelectrical signal. The converted electrical signal works as an inputelectrical signal, and is introduced into the LSI 102 to be processedthere via the adjacent electrical wiring layer 103 b.

(Electro-parallel and Opto-serial Transmission)

The following describes the electro-parallel and opto-serialtransmission, one of actual examples, with reference to FIG. 2. In FIG.2, the reference numeral 202 represents the CPU, 203 a and 203 b theRAMs, 204 the other electronic devices, 207 the parallel electricalwiring formed in the electrical wiring layer, and 208 the optical wiring(optical path) in the optical wiring layer 104.

Normal electrical wiring requires a 64-bit data line comprising sixtransmission paths. Even if low-speed data processing causes no problem,high-speed transmission of a large amount of data (e.g., motionpictures) is susceptible to influences of operations of the otherdevices arranged on the same circuit board or easily causes influencesof EMI. It is very difficult for the conventional wiring to alwaysconstantly transmit data. The optical wiring is used for this purpose.

In FIG. 2, for example, six electrical wiring lines are needed for the64-bit data transmission from the CPU 202 to the RAMs 203 a and 203 b.If the CPU performs a parallel-serial conversion at its last processingstage and one optical I/O element is connected thereto, the electricalsignal is transmitted as a serial optical signal over the opticalwaveguide of the opto-electronic circuit board. The optical signal isreceived and O/E converted at the receiving optical I/O element and thenis serial-parallel converted to generate a 64-bit parallel signal. Whilethe parallel-serial conversion increases the clock, propagation to theoptical waveguide causes no problems of EMI.

While the embodiment selects the optical wiring from the beginning, itis not necessary to always use only the optical wiring. When there isavailable an option of selecting the electrical wiring, it is possibleto make connection by means of the electrical wiring or the opticalwiring depending on needs. This flexibility is one of the majoradvantages major features of the present invention.

The electrical wiring may need to be designed to detour the otherdevices in order to avoid EMI. As a result, the wiring becomes long,causing wiring delay or waveform distortion. In such case, selecting theoptical wiring can provide an EMI-free connection by the shortest route,causing no wiring delay nor waveform distortion.

A device that manages the bus ultimately determines which signal shoulduse the electrical wiring or the optical wiring. The signal convertedinto a light beam propagates by diffusing in the optical wiring layerand approaches the IC arranged at a different location. Near this IC,there is also arranged the photonic ball IC for O/E conversion. Theembodiment arranges the same photonic ball IC. Since its surface isspherical, the beam is directly received by the pn junction surfacewithout using a prism or a mirror, making it possible to very easilymount the photonic ball IC.

According to the embodiment, vias may be formed by piercing the opticalwaveguide layer. Since an optical signal propagates by diffusion,however, its influence is negligible unless the via density becomesexcessively large.

While the embodiment uses the photonic disk IC mounted with theintegrated electronic circuit, it may also be preferable to use a simplering LD or PD, instead, with no electronic circuit integrated. In suchcase, it may be necessary to separately provide a circuit to controlthese devices.

Further, it is possible to manufacture a flexible circuit board by usinga flexible material (e.g., this embodiment) for the electrical wiringlayer and the optical wiring layer.

(Effects)

(1) The optical wiring is available without making a large change in theconventional electrical wiring pattern.

(2) A method compliant with the conventional electrical mounting methodcan be used to mount the E/O device or the O/E device.

(3) The use of the two-dimensional optical waveguide layer (opticalfilm) on the circuit board enables free optical wiring, high-speedtransmission, and EMI-free transmission.

(4) The same signal can be transmitted over the electrical wiring or theoptical wiring depending on uses.

(Embodiment 5)

A photonic disk is provided in each optical wiring layer of themultilayer electronic circuit board.

FIG. 12 schematically shows a sectional view of a fifth embodiment ofthe present invention.

The following mainly describes differences from the fourth embodiment.

(Differences)

(1) Optical wiring layers are multilayered.

(2) No circuit board base is used.

(3) Electronic devices are mounted on both surfaces.

(Common Points)

(1) Each-of optical wiring layers transmits data by diffusing an opticalsignal two-dimensionally.

(2) vias are used to connect electrical wiring layers with each other.

The embodiment is briefly supplemented as follows.

-   -   According to embodiment 1, photonic ball ICs 1108 are mounted at        specified positions on surfaces of electrical wiring layer 1103        a (e.g., PMMA).    -   An optical wiring layer 1104 a is formed on the surface thereof.    -   The photonic ball ICs 1108 are mounted on a second electrical        wiring layer 1103 b which is then bonded to the optical wiring        layer.    -   vias 1109 are provided at specified positions.

By repeating these four processes, it is possible to manufacture amultilayer electronic circuit board comprising alternately layeredelectrical wiring layers and optical wiring layers.

According to the embodiment, all the optical wiring layers comprise asheet-shaped optical waveguide. However, applicable examples are notlimited thereto. For example, it may be preferable to form aone-dimensional optical waveguide that confines light completely.

(Embodiment 6)

A photonic cylinder is provided in a single-layer optical wiring layer.

While the fourth embodiment has described the use of almost the samering LD (PD) structure for the E/O and O/E devices, different structuresmay be used for them. The following describes an example of using acylindrical ring PD instead of the disk-type ring PD.

Compared to the disk type, the cylindrical ring PD has a thick activelayer (e.g., 10 μm). This aims at improving the minimum receivingsensitivity by increasing a light receiving area. Since the active layerthickness is in proportion to the light receiving surface, increasingthe active layer thickness improves the light receiving sensitivity. Inorder to prevent a response speed from being sacrificed, however, it isnecessary to set a high reverse bias voltage.

As mentioned above, the present invention can provide an electroniccircuit board capable of efficient input and output of light to anoptical wiring layer.

1. An electronic circuit board comprising: an optical wiring layersandwiched between two electrical wiring layers, wherein said opticalwiring layer is structured to be a two-dimensional optical waveguide; anE/O device and an O/E device provided in said optical wiring layer or atan interface between said optical wiring layer and said electricalwiring layer, wherein at least one of said E/O device and said O/Edevice is spherical; and a via piercing said optical wiring layer,wherein said via connects said two electrical wiring layers.
 2. Theelectronic circuit board according to claim 1, wherein said electricalwiring layer includes a parallel signal line with an output terminalconnected to said E/O device, and wherein a parallel electrical signaltransmitted in said parallel signal line is parallel-serial converted inan electronic circuit provided in said E/O device and is thentransmitted as a serial optical signal to said optical wiring layer. 3.The electronic circuit board according to claim 2, wherein the serialoptical signal is received by said O/E device, converted into anelectrical signal, serial-parallel converted by an electronic circuitprovided in said O/E device, and then transmitted to a parallel signalline.